Piezoelectric microphone

ABSTRACT

In a device for inspecting watch movements, a piezoelectric contact microphone is supported for engagement with the stem of a watch movement which is urged into axial engagement with the piezoelectric element of the microphone to transmit the vibrations of the watch movement to the element whereby the compressive stresses applied thereto are varied and an output voltage is produced which is adapted to be used in examining the accuracy of the watch movement.

United States Patent Bonny [54] PIEZOELECTRIC MICROPHONE [72] Inventor:Jean-Pierre Bonny, La Chaux-de- Fonds, Switzerland [73] Assignee:Portescop, Le. Porte-Echappement Universal S.A., La Chaux-de- Fonds,Switzerland [22] Filed: Aug. 14, 1970 [21] Appl. No.: 63,710

[30] Foreign Application Priority Data Aug. 27, 1969 Switzerland..13101/69 [52] US. Cl. ..73/6 [51] Int. Cl. ..G04d 7/00 [58] Field ofSearch ..73/6, 67

[5 6] References Cited UNITED STATES PATENTS 2,175,021 10/1939 Gibbs..73/6

2,561,084 7/1951 Wickham ..73/6

[451 Sept. 12, 1972 3,395,566 8/1968 Jucker ..73/6 3,026,708 3/1962Marti ..73/6

OTHER PUBLICATIONS Acoustics by Beranek, copyright 1954, pages 164 to177 Primary Examiner-Louis R. Prince Assistant Examiner-Denis E. CorrAttorney-Curtis, Morris & Safford [57 ABSTRACT In a device forinspecting watch movements, a piezoelectric contact microphone issupported for engagement with the stem of a watch movement which isurged into axial engagement with the piezoelectric element of themicrophone to transmit the vibrations of the watch movement to theelement whereby the com pressive stresses applied thereto are varied andan output voltage is produced which is adapted to be used in examiningthe accuracy of the watch movement.

12 Claims, 5 Drawing Figures PATENTEDSEP 12 Ian 3.690.144

IN VENTOR JEAN-PIERRE BONNV ATT NEY "PIEZOELECTRIC MICROPHONE ment toreceive the vibrations thereof and produce an output voltage'which isadapted to be used in examining the accuracy of the movement.

Apparatus of the above type has been proposed in the past which includesa sound microphone and a sound pick up device such as a crystal orpiezoelectric microphone which is adapted to transform the mechanicalvibrations of the watch movement, caused by the release, drive anddropping impacts of the escapement mechanism, into electrical vibrationsand an output voltage which is utilized in examining the accuracy of themovement. Transformation of watch vibrations into electrical outputvoltage by a piezoelectric crystal has been effected in a variety ofways, the most common of which consists in operatively connecting thecrystal to the watch movement ina position such that the crystal will bevibrated in flexure to produce the deformation of the piezoelectriccrystal element and thereby generate a varying output voltage betweenthe faces of the element.

It has generally been found that in order to obtain maximum sensitivityof piezoelectric microphones which operate in flexure, as describedabove, the crystal used in the microphone must be selected in such amanner that its resonant frequency is within the frequency spectrum ofthe vibrations generated by the watchmovements being inspected. Thefrequency of these vibrations is generally within a range of between andkilocycles, and the crystals are therefore paratus and the stem of awatch movement. It has been found that by thus positioning apiezoelectric element for operation in compression its resonantfrequency is placed outside the frequency spectrum of the vibrations ofwatch movements while at the same time its sensitivity is maintained orincreased. In addition, the piezoelectric microphone is connected to apre-amplifier, as for example an integrated circuit amplifier, whichchosen in accordance with this range. However, a

major difficulty arises with apparatus utilizing piezoelectric crystalsof this type in that the frequency range is excessively selective andnumerous watch movements having vibration frequencies outside this rangecannot be inspected using this type of crystal. To inspect watchmovements which have a vibration frequency spectrum outside the range ofthe piezoelectric element chosen, it has been proposed that an elementhaving a larger resonant frequency, 'which encompasses the frequencyspectrum of the mechanical vibrations of these watch movements, beprovided; however, it has been found that the sensitivity of systemsusing such crystals is severely effected, even to the extent ofrendering the system impractical for use, since the signal-to-noiseratio of such crystals approaches l as their resonant frequencyincreases.

Accordingly, it is an object of the present invention to examine watchmovements with a piezoelectric microphone and to attain a highsignal-to-noise ratio.

It is a further object of the invention to examine watch movementshaving a wide vibration frequency spectrum with a piezoelectric contactmicrophone having a relatively high signal-to-noise ratio.

Another object of the invention is to provide a device for theinspection of watch movements which is both economical and simple inconstruction.

In accordance with an aspect of the present invention, an apparatus forinspecting watch movements includes a piezoelectric element mounted foroperation in compression between a support member on the apis adapted tomatch the impedance of the piezoelectric element to the impedance of theline and thus substantially improve sensitivity and accuracy of thewatch movement inspection apparatus. Moreover, the preamplifier willamplify the electric signal produced by the element to a level, whichfor example may be approximately one volt peak to peak, sufficient todecrease the effects of noise in the transmission line on the output ofthe piezoelectric element. The use of an intermediate pre-amplifier alsoavoids a direct electric coupling between the output of thepiezoelectric element and the input of the amplifier used in theinspection apparatus because the gain and input impedance of theinspection apparatus is thereby substantially reduced.

The above, and other objects, features and advantages of this invention,will be apparent in the following detailed description of illustrativeembodiments thereof which are to be read in connection with theaccompanying drawings, wherein:

FIG. 1 is a schematic illustration of the principal of operation of thepresent invention;

FIG. 2 is a schematic illustration of an embodiment of the presentinvention;

FIG. 3 is a schematic illustration similar to FIG. 2 of anotherembodiment of the present invention;

FIG. 4 is an elevational view, with parts broken away, of a device of atype in which the present invention may be employed; and

FIG. 5 is a sectional view of the support housing for the piezoelectricmicrophone utilized in the embodiment of the invention illustrated inFIG. 4.

Referring now to the drawings in detail, and initially to FIGS. 1 and 2thereof, it will be seen that a piezoelectric element 10 of the typeused in conjunction with the present invention is held, in accordancewith the present invention, in axial compression against a supportmember 12 by a force 14, which is, in one embodiment, applied by directcontact with a watch movement 16. The amplitude of force 14 varies inaccordance with the vibrations of the watch movement as caused by therelease drive and dropping impacts of the escapement mechanisms and whenapplied to element 10, the force vibrates the element in compression andcauses the piezoelectric element to generate a varying electrostaticvoltage between the opposed faces 18 and 20 of the element. The opposedelement faces 18 and 20 are connected by output leads 22 fortransmission of the voltage signal to a device (not shown) whichutilizes the voltage to determine the accuracy of the watch movement 16being tested. By positioning element 10. for operation in compression inthis manner, it isadapted to vibrate within a relatively large frequencyrange to accommodate a wide range of watch movements having varyingvibration frequency spectrums in order to facilitate inspection ofnumerous types of watch movements.

Piezoelectric element 10 is formed of a ceramic material, as forexample, barium titanate. This material is not particularly sensitive totemperature variations in the normal temperature range at which theinspection apparatus is normally used. As a result the inspectionapparatus of the present invention gives highly accurate readings ascompared to the previously proposed devices using crystal piezoelectricelements. Further, element 10 is formed as an elongated cylindricalmember. This configuration provides a high degree of sensitivity whenthe device is operating in compression.

As illustrated schematically in FIG. 2, the force 14 is applied tocompress element 10 by direct contact with stem 24 of watch movement 16.Stem 24 is urged axially against element 10 by compression spring 26which is operatively engaged at its ends between a support member 28 andcrown 25.

As seen in FIG. 3, compressive force 14 may be applied to piezoelectricelement 10 indirectly by a lever mechanism 30 which is operativelyengaged between crown 25 of watch movement 16 and element 10. In thisembodiment lever 30 is pivotally mounted at 32 on a support member 34and has a first end 36 operatively engaged with end 20 of element 10 anda second, opposed, end 38 in contact with crown 25. As in the previouslydescribed embodiment, resilient compression spring 26 is operativelyengaged between support member 28 and crown 25; in this embodiment,however, spring 26 urges stem 24 and crown 25 against lever end 38. Inthis manner, lever end 36 is moved into engagement with face 20 ofelement 10 to compress the element against support portion 12 andthereby transmit vibrations of the watch movement to element 10 in anaxial direction to vary the compressive forces applied thereto.

It is noted that in the embodiment illustrated in FIG. 3 lever 30 may beutilized in accordance with the location of pivot point 32 to amplify ordecrease the vibrations produced by watch movement 16 prior totransmission thereof to element 10.

In each of the embodiments described above, leads 22 are respectivelyconnected at their opposed ends to pre-amplifier 40, which may, forexample be formed as an integrated circuit amplifier. Amplifier 40receives the output voltage produced across the faces of element l andserves to match the impedance of the piezoelectric element to theimpedance of the output lines 42. Lines 42 are connected in theconventional manner to an inspection apparatus (not shown) which isutilized in examining the accuracy of the watch movement. Pre-amplifier40 also serves to amplify the electric signal produced by thepiezoelectric element to a level of about 1 volt, peak to peak, todecrease the effects of noise in transmission line 42 on the output ofelement 10, and moreover, avoids a direct electric coupling betweenelement and the amplifier used in the inspection apparatus itselfwhereby the gain in the input impedance of the latter may besubstantially reduced.

A detailed illustration of a watch support mechanism 50, adapted for usein conjunction with the present invention, is shown in FIG. 4 wherein asupport plateform or base 52 is provided for watch movement 16 whichincludes a housing 54 containing piezoelectric element 10. Watchmovement 16 is seated on a slide member 56 adapted to move laterallywithin support member 52 and urged towards the left in FIG. 4 by spring26 which acts in compression between abutment surface 58 of element 56and wall portion 12 of support platform 52. Slide 56 includes anabutment member 60 which engages watch crown 24 and, by its rigidconstruction with slide 56, cooperates with spring 26 to urge watchmovement 16 against housing 54 and piezoelectric element 10, as will bemore fully described hereinafter. A finger piece 62 is provided on slide56 to facilitate movement of watch movement 16 away from housing 54inorder to remove the watch from the device.

Housing 54 for piezoelectric element 10 is more clearly illustrated inFIG. 5, wherein it is seen that the housing includes a wall portion 64rigidly attached to support platform 52. Piezoelectric element 10, whichis provided with conductive supporting caps 66 and 68 fixed at its ends18 and 20 respectively, is rigidly held at end 18 by engagement of cap66 with abutment members 70 contained within support wall 64. Housing 54is completed by a second support wall 72 which encloses element 10 andincludes an inner annular bore 74. As seen in FIG. 5, an annular ring 76is seated within bore 74 against surface 78 of member 64. Support wall72 includes an annular flange 80 enclosing one end of bore 74 oppositewatch movement 16 and defines an aperture 81 through which a contactpiece 82 extends for engagement with the winding stem 24 of watchmovement 16. Contact piece 82 receives end 20 of element 10 andsupporting caps 68 therein whereby the vibratory forces from watchmovement 16 are transmitted directly to piezoelectric element 10. Member82 includes an annular flange portion 84 which is retained between apair of annular rubber rings 86 and 88, which permit movement of contactpiece 10 with respect to support portion 72. As seen in FIG. 5, ring 86is engaged between flange 84 and surface of ring 76 to limit themovement of contact piece 82 and ring 88 is engaged between flange 84and flange 80 to further limit movement of contact piece 82 and alsoprovide support therefore in the manner illustrated. Rings 86 and 88serve to isolate vibrations transmitted through contact piece 82 fromthe ring 76 and frame member 72 during transmission to element 10 toassure their complete transmission to the piezoelectric ele ment throughmetal supporting caps 66 and 68. These caps provide electricalconnection between the ends 18 and 20 of element 10 and wires 22, whichin turn are connected to pre-amplifier 40 to transmit the varyingvoltages produced by vibration of element 10. As seen in the drawings,one of the wires 42 leading from preamplifier 40 is connected to supportplatform 52 as a ground lead, whereas the other lead extends through thehousing to a point of connection with the inspection apparatus.

By placing stem 24 of watch movement 16 in direct engagement withelement 10 vibrations from within the watch movement are directlytransmitted to the element. As a result the resolution of thesevibrations is increased, i.e., the vibrations produced by the variousimpacts in the escape mechanism can be distinguished more easily and thesignal produced by element 10 contains more detail.

It is thus seen that a relatively simple apparatus has been provided foruse in determining the accuracy of a variety of watch movements.Construction of apparatus in accordance with the present inventionfacilitates the use of a piezoelectric element, which is held incompression to increase the relative frequency spectrum thereof in orderto permit inspection and testing of a large range of watch movements.

Although illustrative embodiments of the presentinvention have beendescribed herein with reference to the accompanyingdrawings, it is to beunderstood that the invention is not limited to those preciseembodiments, and the various changes and modifications may be effectedtherein by one skilled in the art without departing from the scope orspirit of this invention.

What is claimed is:

l. A device for inspecting watch movements having operating stems, saiddevice comprising a base for supporting a watch movement in a relativelyfixed position, a piezoelectric element having first and second endportions and adapted to produce an output voltage when vibrated incompression along the axis between said ends, a rigid support memberengaging said first end portion of said piezoelectric element andholding said first end portion in a relatively fixed position againstaxial movement thereof, means operatively engaged between a watchmovement on said base and said second end portion-of said element forholding said element in compression against said rigid support memberand for transmitting vibrations from said watch movement to said elementto thereby vary the compressive stresses against said element, andresilient means urging said watch into contact with said meansoperatively engaged between said watch movement and said second endportion of said element, whereby said element produces an output signalrepresentative of said vibrations.

2. A device as defined in claim 1 including a pre-amplifier operativelyconnected to said piezoelectric element.

' 3. A device as defined in claim 1 wherein said piezoelectric elementis formed of a ceramic material.

4. A device as defined in claim 3 wherein said ceramic material isbarium titanate.

5. A device as defined in claim 3 wherein said element is formed as anelongated cylindrical member.

6. A device as defined in claim 1 wherein said means operatively engagedbetween said watch movement and said piezoelectric element is positionedto contact the stem of a watch movement placed on said base wherebyvibrations in said watch movement are transmitted directly through saidstem to said crystal.

7. A device as defined in claim 6 wherein said resilient means comprisesa compression spring operatively engaged between the crown of said watchmovement and a portion of said base.

8. A device as defined in claim 1 wherein said means operatively engagedbetween said watch movement and said second end portion of saidpiezoelectric element includes a pivotally mounted arm memberoperatively engaged between said second end portion of the element andthe watch movement, said resilient means being positioned to urge saidwatch movement into contact with said arm member to pivot said arm andcompress said piezoelectric element, whereby vibrations of said watchmovement are transmitted to said element through pivotal movements ofsaid arm b mg A device as defined in claim 8 wherein said resilientmeans comprises a compression spring operatively engaged between saidwatch movement and a portion of said base.

10. A device as defined in claim 1 including a housing mounted on saidbase member, with said rigid support member forming one wall of saidhousing and said element being contained therein, said means fortransmitting vibrations comprising a contact member slidably mounted insaid housing and having one end engaged with said second end portion ofsaid element and the opposite end thereof positioned toengage the stemof the watch movement.

11. A device as defined in claim 10 wherein said other end of saidcontact member is recessed to receive said watch stem.

12. A device as defined in claim 11 wherein said contact member isgenerally cylindrical and has an annular flange formed thereon adjacentsaid one end thereof, said housing including a first resilient ringsurrounding said contact member adjacent, said flange and a secondresilient ring surrounding said element on the other side of said flangeto isolate vibrations transmitted through said contact member from saidhousing and assure their transmission to said element.

1. A device for inspecting watch movements having operating stems, saiddevice comprising a base for supporting a watch movement in a relativelyfixed position, a piezoelectric element having first and second endportions and adapted to produce an output voltage when vibrated incompression along the axis between said ends, a rigid support memberengaging said first end portion of said piezoelectric element andholding said first end portion in a relatively fixed position againstaxial movement thereof, means operatively engaged between a watchmovement on said base and said second end portion of said element forholding said element in compression against said rigid support memberand for transmitting vibrations from said watch movement to said elementto thereby vary the compressive stresses against said element, andresilient means urging said watch into contact with said meansopEratively engaged between said watch movement and said second endportion of said element, whereby said element produces an output signalrepresentative of said vibrations.
 2. A device as defined in claim 1including a pre-amplifier operatively connected to said piezoelectricelement.
 3. A device as defined in claim 1 wherein said piezoelectricelement is formed of a ceramic material.
 4. A device as defined in claim3 wherein said ceramic material is barium titanate.
 5. A device asdefined in claim 3 wherein said element is formed as an elongatedcylindrical member.
 6. A device as defined in claim 1 wherein said meansoperatively engaged between said watch movement and said piezoelectricelement is positioned to contact the stem of a watch movement placed onsaid base whereby vibrations in said watch movement are transmitteddirectly through said stem to said crystal.
 7. A device as defined inclaim 6 wherein said resilient means comprises a compression springoperatively engaged between the crown of said watch movement and aportion of said base.
 8. A device as defined in claim 1 wherein saidmeans operatively engaged between said watch movement and said secondend portion of said piezoelectric element includes a pivotally mountedarm member operatively engaged between said second end portion of theelement and the watch movement, said resilient means being positioned tourge said watch movement into contact with said arm member to pivot saidarm and compress said piezoelectric element, whereby vibrations of saidwatch movement are transmitted to said element through pivotal movementsof said arm member.
 9. A device as defined in claim 8 wherein saidresilient means comprises a compression spring operatively engagedbetween said watch movement and a portion of said base.
 10. A device asdefined in claim 1 including a housing mounted on said base member, withsaid rigid support member forming one wall of said housing and saidelement being contained therein, said means for transmitting vibrationscomprising a contact member slidably mounted in said housing and havingone end engaged with said second end portion of said element and theopposite end thereof positioned to engage the stem of the watchmovement.
 11. A device as defined in claim 10 wherein said other end ofsaid contact member is recessed to receive said watch stem.
 12. A deviceas defined in claim 11 wherein said contact member is generallycylindrical and has an annular flange formed thereon adjacent said oneend thereof, said housing including a first resilient ring surroundingsaid contact member adjacent, said flange and a second resilient ringsurrounding said element on the other side of said flange to isolatevibrations transmitted through said contact member from said housing andassure their transmission to said element.